1. Technical Field
This invention relates to a zoom lens that employs aspheric lenses.
2. Related Art
In the imaging device of a video camera or the like, a zoom lens with a wide field angle is commonly used. In the past, many zoom lenses of this type had a four-group constitution with refractive power that is positive, negative, positive, and positive, in order from the object side. In a four-group constitution zoom lens, with the first lens group and the third lens group fixed, the second lens group is moved in the optical axis direction to change the magnification (zoom); and the fourth lens group is moved to correct variation of the image surface that occurs with displacement and is moved in the optical axis direction to focus. This so-called four-group focus zoom method is currently the most common one.
Various types of zoom lenses of this kind have been proposed. For example, it has been attempted to make a wider angle and to suppress distortion by using a four-lens constitution for the first lens group, and by making the aperture independently movable.